Transmission ratio variable mechanism and motor vehicle steering system including the same

ABSTRACT

A transmission ratio variable mechanism is provided with: an input member and an output member capable of rotation about a first axis; an inner race for differentially rotatably coupling to each member; an outer race for rotatably supporting the inner race via a rolling element; and a transmission ratio variable mechanism-use electric motor for rotation-driving the outer race. A second axis which is a center line of the inner race and the outer race is inclined to the first axis. A first concave-convex engaging section for engaging one side end surface of the inner race and a power transmission surface of the input member corresponding to the one end surface are arranged. There is provided a second concave-convex engaging section for engaging the other end surface of the inner race and a power transmission surface of the output member.

TECHNICAL FIELD

The present invention relates to a transmission ratio variable mechanismcapable of changing a transmission ratio of a steered angle of steeredwheels to a steering angle of a steering member, and also relates to amotor vehicle steering system including the same.

BACKGROUND ART

There is known a motor vehicle steering system including a transmissionratio variable mechanism capable of changing a transmission ratio of anoutput rotation angle to an input rotation angle (for example, seePatent Documents 1 and 2).

In the motor vehicle steering system in Patent Document 1, between anupper steering shaft coupled to a steering wheel and a lower steeringshaft coupled to a steering gear, there is arranged a toothed-gearreducer including toothed gears of which tooth sections are formed of“rollers.” In each “roller” the both ends are held by a retainer, andare rotatable to a toothed gear main body.

The transmission ratio variable mechanism arranged in this toothed-gearreducer is provided with a first toothed gear of which the rotation isrestrained by the upper steering shaft, a fourth toothed gear of whichthe rotation is restrained by the lower steering shaft, and a swingingtoothed gear having an axis inclined to rotation axis of the first andfourth toothed gears. At the both ends of an outer toothed gear sectionof a swinging toothed gear, there are formed second and third toothedgears, and the second toothed gear is meshed with the first toothed gearand the third toothed gear is meshed with the fourth toothed gear.

-   Patent Document 1: Japanese Published Unexamined Patent Application    No. 2006-82718-   Patent Document 2: Japanese Published Unexamined Patent Application    No. 2007-170624

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In the structure in Patent Document 1, at the both ends of the outertoothed gear section of the swinging toothed gear, there are formed thesecond and third toothed gears. Thus, diameters of the second and thirdtoothed gears are large. Therefore, a radial direction support span islong in an axial direction where the outer toothed gear section issupported by the first and fourth toothed gears from the both ends, anda supporting rigidity of the outer race toothed gear section isdecreased. Moreover, as a result of large diameters of the second andthird toothed gears, circumferential speeds of the second and thirdtoothed gears when being driven are fast, resulting in a large meshingsound.

Further, in the structure in Patent Document 1, there is arranged anaxial direction force imparting member for imparting one of the firstand fourth toothed gears with an axial direction force on the swingingtoothed gear side. However, the second and third toothed gears in largediameter are formed at the both ends of the outer toothed gear sectionof the swinging toothed gear. Thus, when the outer toothed gear sectionhaving such a large diameter is supported by the first and fourthtoothed gears from the both sides in the axial direction, the supportspan with respect to the radial direction becomes long. Thus, adeformation of the swinging toothed gear becomes large by the axialdirection force. As a result, a biasing force acted on the meshingsection between the toothed gears meshed to each other is weakened.

Moreover, in the structure in Patent Document 1, in addition to a needfor using the “rollers” equal in number to those of the teeth, there isa need for using the retainer. Thus, the number of components is madelarge. When the number of components is large, it takes time and effortto assemble. Further, it takes time and effort to secure sufficientassembly accuracy.

The present invention has been achieved in view of these circumstances,and an object thereof is to provide a transmission ratio variablemechanism capable of increasing the supporting rigidity of thetransmission ratio variable mechanism and of decreasing the drivingnoise, and also to provide a motor vehicle steering system including thesame.

Another object of the present invention is to provide a transmissionratio variable mechanism capable of imparting a sufficient preload and amotor vehicle steering system including the same.

Another object of the present invention is to provide a motor vehiclesteering system capable of decreasing the number of components and alsodecreasing time and effort required for assembly.

Means for Solving the Problem

In the following description, reference numerals in parenthesesrepresent reference numerals of the corresponding constituent elementsin the following embodiment. However, it is not intended to limit thescope of the claims by these reference numerals.

To achieve the above-described object, a transmission ratio variablemechanism (5) of the present invention is the transmission ratiovariable mechanism (5) capable of changing a transmission ratio (θ2/θ1)of a steered angle (82) of steered wheels (4L, 4R) to a steering angle(θ1) of a steering member (2), is provided with: an input member (20)and an output member (22) capable of rotation about a first axis (A); afirst bearing ring (391), having first and second end surfaces (71, 73),for differentially rotatably coupling the input member (20) and theoutput member (22); a second bearing ring (392) for rotatably supportingthe first bearing ring (391) via a rolling element (393); and anactuator (23) capable of rotation-driving the second bearing ring (392).

A second axis (B) being a center line of the first bearing ring (391)and the second bearing ring (392) is inclined to a first axis (A), theinput member (20) and the output member (22) respectively have powertransmission surfaces (70, 72) opposite the first and second endsurfaces (71, 73) of the first bearing ring (391).

Moreover, a first concave-convex engaging section (64) and a secondconcave-convex engaging section (67) are arranged forpower-transmittably engaging each end surface (71, 73) of the firstbearing ring (391) and the power transmission surfaces (70, 72)corresponding to the end surfaces (71, 73). The first concave-convexengaging section (64) and the second concave-convex engaging section(67) include convex portions (65, 68; 65A) arranged on each end surface(71, 73) and on one of the power transmission surfaces (70, 72)corresponding to the end surfaces, and concave portions (66, 69; 66A;66B) arranged on an alternate surface and engaged with the convexportions.

According to the configuration, the input member (20), the first bearingring (391), and the output member (22) are aligned in a direction inwhich the first axis (A) extends. Thus, the transmission ratio variablemechanism (5) can be made compact with respect to radial directions (R1,R2) of the input member (20) and the output member (22). As a result,the transmission ratio variable mechanism (5) can be made more compact.

Further, the first concave-convex engaging section (64) and the secondconcave-convex engaging section (67) are arranged on a side of the firstbearing ring (391). The first bearing ring (391) is supported by theinput member (20) and the output member (22) from both sides of theaxial direction. Thereby, a support structure of the first bearing ring(391) can be decreased in size in the radial direction. Thereby, thesupporting rigidity of the first bearing ring (391) also can beincreased. A convex portion or a concave portion of the firstconcave-convex engaging section (64) and the second concave-convexengaging section (67) are arranged on a side of the first bearing ring(391). Thereby, the circumferential speed of driving the convex portionor the concave portion arranged in the first bearing ring (391) can bedecreased. Thus, an engaging noise generated between the firstconcave-convex engaging section (64) and the second concave-convexengaging section (67) can be decreased.

In the present invention, the actuator may include an electric motor(23). The electric motor (23) may include a rotor (231) for corotatablyholding the second bearing ring (392) and capable of rotation about thefirst axis (A). In this case, the second bearing ring (392) can besurrounded by the rotor (231). Thus, the rotor (231), the firstconcave-convex engaging section (64), and the second concave-convexengaging section (67) can be placed at a position overlapping withrespect to a direction in which the first axis (A) extends, therebyachieving further compactness of the device.

The rotor (231) is preferably formed in a tubular shape surrounding thefirst concave-convex engaging section (64) and the second concave-convexengaging section (67). In this case, the rotor (231) may be used as asoundproof wall. Thus, it is possible to inhibit an engaging noisegenerated between the first concave-convex engaging section (64) and thesecond concave-convex engaging section (67) from being transmitted tothe outside of the rotor (231). As a result, noise can be furtherdecreased.

Moreover, in the present invention, there is a case that the rotor (231)is formed with an inclined hole (63), having a center line along thesecond axis (B), for holding the second bearing ring (392). In thiscase, the inclined hole (63) of the rotor (231) is caused to hold thesecond bearing ring (392), and thereby, the second axis (B) as a centerline of the second bearing ring (392) can be inclined to the first axis(A).

There is a configuration that the rotor (231) is both-end supported by asecond bearing (32) and a fourth bearing (34) held by a housing (24).The first bearing ring (391) is placed between the second bearing (32)and the fourth bearing (34) with respect to an axial direction of therotor (231). In this configuration, the rotor (231) can be both-endsupported by a pair of bearings (32, 34). Thus, the supporting rigidityof the rotor (231) can be increased. Moreover, the first bearing ring(391) is placed between the pair of bearings (32, 34). Thus, the rotor(231) for receiving force from the first bearing ring (391) can befirmly supported, thereby the rotor (231) is prevented from runoutthereof. As a result, it is possible to contribute to a decrease innoise.

The second bearing (32) and the fourth bearing (34) may movably supportthe rotor (231) with respect to the axial direction of the rotor (231).In this case, along with the movement of the first bearing ring (391) inthe axial direction of the rotor (231), the second bearing ring (392)and the rotor (231) can be moved together in the axial direction with ofthe rotor (231). As a result, an unnecessary force is prevented frombeing acted between the first bearing ring (391) and the second bearingring (392).

In the present invention, it is possible to adopt a structure including:a first shaft (11) inserted through a through hole (202 a) formed in theinput member (20) and corotatably connected to the input member (20); asecond shaft (12) inserted through a through hole (22 a) formed in theoutput member (22) and corotatably connected to the output member (22);and a support mechanism (133) for coaxially, relatively rotatablysupporting mutual opposite end sections (11 a, 12 a) of the first andsecond shafts (11, 12). In this structure, when the mutual opposite endsections (11 a,12 a) of the first and second shafts (11,12) arecoaxially supported, the mutual coaxiality of the first and secondshafts (11,12) can be improved. As a result, the input member (20) andthe output member (22) can be prevented from shaft swing with respect toothers, and an unexpected change in the state of engagement between theconvex portion and the concave portion in each concave-convex engagingsection (64, 67) can be inhibited. Thereby an engaging sound isprevented from an increase thereof.

In the present invention, the support mechanism (133) may include: atubular member (202; 202D) that surrounds the mutual opposite endsections of the first and second shafts (11, 12) and that is corotatablycoupled to one of the first and second shafts (11, 12); and a bearing(38), interposed between an alternate one of the first and second shafts(11, 12) and the tubular member (202; 202D), for permitting relativerotation of the both components. In this configuration, the supportmechanism (133) can be realized by a simple configuration using thetubular member (202; 202D) and the bearing (38). Moreover, thearrangement of the bearing (38) between the first shaft (11) and thesecond shaft (12) makes the relative rotation between the first andsecond shafts (11, 12) smooth.

In the present invention, it is possible to adopt a structure that thetransmission ratio variable mechanism (5) includes a biasing member(113) for biasing in a bias direction (H) in which one of the inputmember (20) and the output member (22) is brought close to an alternateone of the input member (20) and the output member (22), and a preloadis imparted to the first concave-convex engaging section (64) and thesecond concave-convex engaging section (67) by the biasing member (113).According to the structure, in the respective first concave-convexengaging section (64) arranged on a side of the first end surface of thefirst bearing ring (391) and second concave-convex engaging section (67)arranged on a side of the second end surface, the preload is impartedbetween the convex portion and the concave portion. Thereby, in eachconcave-convex engaging section (64, 67), backlash between the convexportion and the concave portion can be prevented from occurringtherefrom, and thus, an engaging noise can be decreased.

The biasing member (113) may bias the input member (20) toward theoutput member (22). In this case, the biasing force of the biasingmember (113) can be transmitted in the order of: the input member (20),the first concave-convex engaging section (64) arranged on a side of thefirst end surface of the first bearing ring (391), the secondconcave-convex engaging section (67) arranged on a side of the secondend surface of the first bearing ring (391), and the output member (22).

In the present invention, the transmission ratio variable mechanism (5)may include a first bearing (31), held by a housing (24; 24C), forrotatably supporting the input member (20), in which the biasing member(113) may bias the input member (20) via the first bearing (31). In thiscase, the preload can be imparted to the first bearing (31) by thebiasing member (113). Thus, an abnormal noise resulting from the bearing(31) can be prevented from being generated therefrom.

The first bearing (31) may be held by a bearing holding hole (134)arranged in the housing (24), and the biasing member (113) may include ascrew member (113) engaged with a screw section (134 a) formed in thebearing holding hole (134). In this case, the biasing force by the screwmember (113) can be adjusted by adjusting an amount of screwing thescrew member (113) into the screw section (134 a).

In the present invention, the first bearing (31) may include an outerrace (312) held rotatably by the bearing holding hole (134) and movablyin an axial direction and an inner race (311) that can be rotated andmoved together in the axial direction with the input member (20), andthe screw member (113) may press against an end surface of the outerrace (312). In this case, the biasing force of the screw member (113)can be transmitted to the inner race(311) via the outer race (312).Thus, the preload can be reliably imparted to the first bearing (31).

In the present invention, the transmission ratio variable mechanism (5)may include a third bearing (33), held by a housing (24), for rotatablysupporting the output member (22), in which movement of the outputmember (22) in a bias direction may be regulated by the third bearing(33). In this case, a force that the output member (22) makes movementin the bias direction can be received by the third bearing (33). Thus,the preload can be imparted to the third bearing (33).

In the present invention, the input member (20) and the output member(22) may include opposite surfaces that are opposed to each other(136,137) by arranging a gap (138) in a direction parallel to the firstaxis (A). In this case, when the input member (20) and the output member(22) are brought close to each other by the biasing force of the biasingmember (113), contacting of the opposite surfaces can be inhibited.

In the transmission ratio variable mechanism (5) of the presentinvention, the convex portion and the concave portion of eachconcave-convex engaging section (64, 67) may be respectively formedintegrally with a corresponding member, out of the input member (20),the first bearing ring (391), and the output member (22).

A more specific example is a structure in which: the first convexportion (65) of the first concave-convex engaging section (64) isconstantly formed with the power transmission surface of the inputmember (20); the first concave portion (66) is integrally formed withthe first end surface of the first bearing ring (391); the second convexportion (68) of the second concave-convex engaging section (67) isintegrally formed with the power transmission surface of the outputmember (22); and the second concave portion (69) is integrally formedwith the second end surface of the first bearing ring (391).

According to the structure, it is not necessary to separately prepare aholding member for holding the convex portion, and thus, the number ofcomponents of the transmission ratio variable mechanism (5) can bereduced. Further, as the number of components is small, the assembly ofthe transmission ratio variable mechanism (5) can be facilitated.Further, the respective convex portion and concave portion of eachconcave-convex engaging section (64, 67) are integrally formed with thecorresponding member, and thus, the accuracy for assembling the mutualcomponents can be more easily enhanced as compared to a case that theconvex portion and the concave portion are formed separately of thecorresponding member.

The integrated formation by using a single material enables collectiveformation of each convex portion (each concave portion) and thecorresponding member, and thus, the number of manufacturing process canbe reduced.

At a base end section of the first convex portion (65) and/or a base endsection of the second convex portion (68), a relieving section (75) foravoiding contact with a corresponding concave portion is preferablyarranged. For example, the relieving section (75) may be realized byforming a trench that runs through the input member (20) in the radialdirection at the base end section of the first convex portion (65), andby forming a trench that runs through the output member (22) in theradial direction at the base end section of the second convex portion(68). With a structure in which the relieving section (75) is arranged,when each of the first and second convex portions (65, 68) is engagedwith the corresponding concave portion, undercut in each of the firstand second convex portions (65, 68) can be prevented from the occurrencethereof, thereby inhibiting wear of each convex portion and each concaveportion.

The present invention may be configured so that the input member (20),the output member (22), and the first bearing ring (391) arerespectively annular, and the first convex portion (65), the secondconvex portion (68), the first concave portion (66), and the secondconcave portion (69) respectively extend toward radial directions (R1,R2) and have progressively increasing widths (F1, F2) with respect tocircumferential directions (C1, C2) from an inside of the radialdirection toward an outside thereof. In this case, out of the convexportion and the concave portion, the more outwardly of the radialdirection of the corresponding members, the wider the widths (F1, F2) inthe circumferential directions (C1, C2). As a result, the sliding of theboth concave portions and the convex portions in the mutual engagementcan be reduced. Thereby, the durability of the respective concaveportion and convex portion can be made longer.

The first convex portion (65) and the first concave portion (66) mayinclude first contact regions (76, 79) that come into contact with eachother, the second convex portion (68) and the second concave portion(69) may include second contact regions (76, 79) that come into contactwith each other, and near the first contact regions and/or the secondcontact regions, lubricant holding sections (78, 82) may be respectivelyarranged. In this case, from near the contact regions, the lubricant canbe supplied to the contact regions, and thus, the engagement between theconvex portion and the concave portion can be made smoother.

Moreover, with a configuration that the first convex portion (65) and/orthe first concave portion (66) are formed by using a low frictionmaterial for decreasing a friction resistance. The second convex portion(68) and the second concave portion (69) are formed by using a lowfriction material for decreasing a friction resistance, the frictionresistance generated when the concave portion and the convex portion areengaged can be further decreased.

The motor vehicle steering system of the present invention includes anyone of the above-described transmission ratio variable mechanisms (5)and has a steering member coupled to the input member (20) and a turningmechanism coupled to the output member (22). In this case, the operationof the steering member by a driver can be corrected by the transmissionratio variable mechanism (5).

Further, when a steering-assist-force imparting mechanism (19) forimparting a steering assist force is further provided, it becomespossible to reduce a force required by the driver for steering.

The above-described and/or other advantages, characteristics, andeffects of the present invention will be made clear from the descriptionof the embodiment below with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a schematic configuration of a motor vehiclesteering system including a transmission ratio variable mechanismaccording to one embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a specific configuration inwhich a transmission ratio variable mechanism and asteering-assist-force imparting mechanism are accommodated in a housing.

FIG. 3 is an enlarged view of a transmission ratio variable mechanism ofFIG. 2 and a surrounding area thereof.

FIG. 4 is a lateral side view showing the transmission ratio variablemechanism of which the one portion is expressed in cross section.

FIG. 5 is a perspective view of an input member main body and an innerrace.

FIG. 6 is a perspective view showing relevant parts of the input membermain body and the inner race.

FIG. 7 is a cross-sectional view showing engagement between a firstconvex portion and a first concave portion.

FIG. 8 is a perspective view showing relevant parts of anotherembodiment of the present invention.

FIG. 9 is a cross-sectional view showing relevant parts of still anotherembodiment of the present invention.

FIG. 10 is a cross-sectional view showing relevant parts of yet stillanother embodiment of the present invention.

FIG. 11 is a cross-sectional view showing relevant parts of anotherembodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 . . . motor vehicle steering system; 2 . . . steering member;        4R and 4L . . . turning wheel; 5 . . . transmission ratio        variable mechanism; 10 . . . turning mechanism; 12 . . . second        shaft (input shaft); 13 . . . third shaft (output shaft); 19 . .        . steering-assist-force imparting mechanism; 20 . . . input        member; 22 . . . output member; 23 . . . transmission ratio        variable mechanism-use motor (actuator; electric motor); 24 . .        . housing (steering column); 44 . . . torque sensor (torque        detecting means); 64 . . . first concave-convex engaging        section; 65 and 65A . . . first convex portion; 66, 66A, and 66B        . . . first concave portion; 67 . . . second concave-convex        engaging section; 68 . . . second convex portion; 69 . . .        second concave portion; 70 . . . power transmission surface (of        input member); 71 . . . first end surface; 72 . . . power        transmission surface (of output member); 73 . . . second end        surface; 231 . . . rotor; 391 . . . inner race; 392 . . . outer        race; 393 . . . rolling element; A . . . first axis; B . . .        second axis; θ1 . . . steering angle; θ2 . . . steered angle;        and θ2/θ1 . . . transmission ratio.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a diagram showing a schematic configuration of a motor vehiclesteering system 1 including a transmission ratio variable mechanism,according to one embodiment of the present invention.

The motor vehicle steering system 1 applies a steering torque impartedto a steering member 2 such as a steering wheel to each of right andleft steered wheels 4R and 4L via a steering shaft 3, etc., as asteering shaft (steering axle), so as to perform turning. The motorvehicle steering system 1 has a VGR (Variable Gear Ratio) functioncapable of changing a transmission ratio θ2/θ1, which is a ratio ofsteered angle θ2 of steered wheels relative to a steering angle θ1 of asteering member 2.

The motor vehicle steering system 1 includes: the steering member 2; andthe steering shaft 3 connected to the steering member 2. The steeringshaft 3 includes first to third shafts 11 to 13 placed on the same shaftas one another. A first axis A, which is a center line of each of thefirst to third shafts 11 to 13, also serves as a rotation axis of eachof the first to third shafts 11 to 13.

One end of the first shaft 11 is corotatably coupled with the steeringmember 2. Herein, the “one end” refers to an upstream end section wherethe steering member 2 exists, and the “other end” refers to a downstreamend section where the steered wheels 4R and 4L exist. The other end ofthe first shaft 11 and one end of the second shaft 12 are differentiallyrotatably coupled via a transmission ratio variable mechanism 5. Theother end of the second shaft 12 and one end of the third shaft 13 areelastically coupled relatively rotatably and power-transmittably withina predetermined range via a torsion bar 14. The other end of the thirdshaft 13 is connected via a universal joint 7, an intermediate shaft 8,a universal joint 9, a turning mechanism 10, etc., to the steered wheels4R and 4L.

The turning mechanism 10 includes: a pinion shaft 15 coupled to theuniversal joint 9; and a rack shaft 16 that is provided with a rack 16 ameshed with a pinion 15 a at a leading end of the pinion shaft 15 andthat serves as a steered shaft extending in the left and rightdirections of a motor vehicle. To a pair of end sections of the rackshaft 16, knuckle arms 18R and 18L are coupled via tie rods 17R and 17L,respectively.

With the aforementioned configuration, the rotation of the steeringmember 2 is transmitted to the turning mechanism 10 via the steeringshaft 3, etc. In the turning mechanism 10, the rotation of the pinion 15a is converted into axial direction motion of the rack shaft 16. Theaxial direction motion of the rack shaft 16 is transmitted to thecorresponding knuckle arms 18R and 18L via each of the tie rods 17R and17L. As a result, the knuckle arms 18R and 18L are respectively pivoted.Thereby, the corresponding wheels 4R and 4L coupled to each of theknuckle arms 18R and 18L are steered and oriented, respectively.

The transmission ratio variable mechanism 5 is for changing a rotationtransmission ratio (transmission ratio θ2/θ1) between the first andsecond shafts 11 and 12 of the steering shaft 3. The transmission ratiovariable mechanism 5 includes: an input member 20 arranged at the otherend of the first shaft 11; an output member 22 arranged at one end ofthe second shaft 12; and a bearing ring unit 39 interposed between theinput member 20 and the output member 22.

The input member 20 is coupled coaxially and corotatably to the steeringmember 2 and the first shaft 11, and the output member 22 is coupledcoaxially and corotatably to the second shaft 12. The first axis Aserves also a center line and a rotation axis of the input member 20 andthe output member 22.

The output member 22 is connected via the second shaft 12, the turningmechanism 10, etc., to the steered wheels 4R and 4L.

The bearing ring unit 39 includes an inner race 391 as a first bearingring, an outer race as a second bearing ring, and a rolling element 393interposed between the inner race 391 and the outer race, whereby afour-point contact bearing is configured.

Examples of the rolling element 393 include a ball, a cylindricalroller, a needle roller, and a tapered roller. The rolling element maybe installed in a single row or installed in a double row. Wheninstalled in a double row, the inner race 391 can be prevented fromexcess inclination. An example of the rolling element 393 in a doublerow includes a double-row angular contact bearing.

The inner race 391 is for differentially rotatably coupling the inputmember 20 and the output member 22. The inner race 391 and the outerrace include a second axis B as a center line inclined to the first axisA. The inner race 391, which is rotatably supported to the outer race,as a second bearing ring, via the rolling element 393, is rotatableabout the second axis B. Moreover, the outer race, along with driving ofa transmission ratio variable mechanism-use motor 23 as an electricmotor for driving the outer race, is rotatable about the first axis A.The inner race 391 and the outer race are capable of coriolis motion(wobbling) about the first axis A.

The transmission ratio variable mechanism-use motor 23 is placed outwardin a radial direction about the first axis A of the bearing ring unit39. The transmission ratio variable mechanism-use motor 23 changes thenumber of rotations of the outer race about the first axis A thereby tochange the transmission ratio θ2/θ1.

The transmission ratio variable mechanism-use motor 23 is a brushlessmotor placed coaxially to the steering shaft 3, for example, andincludes a rotor 231 for holding the bearing ring unit 39 and a stator232 that surrounds the rotor 231 and that is fixed to a housing 24 as asteering column. The rotor 231 is designed to rotate about the firstaxis A.

The motor vehicle steering system 1 is provided with asteering-assist-force imparting mechanism 19 for imparting the steeringshaft 3 with a steering assist force. The steering-assist-forceimparting mechanism 19 includes: the second shaft 12 as an input shaftconnected to the output member 22 of the transmission ratio variablemechanism 5; the third shaft 13 as an output shaft connected to theturning mechanism 10; a torque sensor 44, described later, for detectingtorque that is transmitted between the second shaft 12 and the thirdshaft 13; a steering assisting motor 25 as a steering assistingactuator; and a reduction gear mechanism 26 interposed between thesteering assisting motor 25 and the third shaft 13.

The steering assisting motor 25 is an electric motor such as a brushlessmotor. Output of the steering assisting motor 25 is transmitted via thereduction gear mechanism 26 to the third shaft 13.

The reduction gear mechanism 26 is formed by a worm gear mechanism, forexample, and includes a worm shaft 27 as a driving toothed gear coupledto the output shaft 25 a of the steering assisting motor 25 and a wormgear 28 as a driven toothed gear that is meshed with the worm shaft 27and coupled corotatably to the third shaft 13. Moreover, the reductiongear mechanism 26 is not limited to the worm gear mechanism, and may beselected from other toothed gear mechanisms such as a parallel-axis gearmechanism using a spur gear or a spiral gear.

The transmission ratio variable mechanism 5 and thesteering-assist-force imparting mechanism 19 are arranged in the housing24, and accommodated within the housing 24. The housing 24 is placedwithin a passenger compartment (cabin) of a motor vehicle. Moreover, thehousing 24 may be placed to surround the intermediate shaft 8 or may beplaced within an engine room of the motor vehicle.

Driving of the transmission ratio variable mechanism-use motor 23 andthe steering assisting motor 25 are respectively controlled by a controlsection 29 having a CPU, a RAM, and a ROM. The control section 29 isconnected via a driving circuit 40 to the transmission ratio variablemechanism-use motor 23, and also, connected via a driving circuit 41 tothe steering assisting motor 25.

The control section 29 is connected with a steering angle sensor 42, amotor resolver 43 as a rotation-angle detecting means for detecting therotation angle of the transmission ratio variable mechanism-use motor23, a torque sensor 44 as a torque detecting means, a steered anglesensor 45, a vehicle speed sensor 46, and a yaw rate sensor 47,respectively.

From the steering angle sensor 42, a signal in relation to the rotationangle of the first shaft 11, as a value corresponding to the steeringangle θ1 which is an operation amount from a direct advance position ofthe steering member 2, is input to the control section 29.

From the motor resolver 43, a signal in relation to a rotation angle θrof the rotor 231 of the transmission ratio variable mechanism-use motor23 is input.

From the torque sensor 44, as a value corresponding to a steering torqueT acted on the steering member 2, a signal in relation to torque actedbetween the second and third shafts 12 and 13 is input.

From the steered angle sensor 45, as a value corresponding to thesteered angle θ2, a signal in relation to the rotation angle of thethird shaft 13 is input.

From the vehicle speed sensor 46, a signal in relation to a vehiclespeed V is input.

From the yaw rate sensor 47, a signal in relation to a yaw rate γ of themotor vehicle is input.

The control section 29 controls driving of the transmission ratiovariable mechanism-use motor 23 and the steering assisting motor 25based on the signals, etc., of the sensors 42 to 47.

With the aforementioned configuration, the output of the transmissionratio variable mechanism 5 is transmitted via the steering-assist-forceimparting mechanism 19 to the turning mechanism 10. More specifically,the steering torque input to the steering member 2 is input via thefirst shaft 11 to the input member 20 of the transmission ratio variablemechanism 5, and then, transmitted from the output member 22 to thesecond shaft 12 of the steering-assist-force imparting mechanism 19. Thesteering torque transmitted to the second shaft 12 is transmitted to thetorsion bar 14 and the third shaft 13, and after being mixed with theoutput from the steering assisting motor 25, transmitted via theintermediate shaft 8, etc., to the turning mechanism 10.

FIG. 2 is a cross-sectional view showing a more specific configurationof the relevant parts in FIG. 1. With reference to FIG. 2, the housing24 is configured by forming a metal such as an aluminum alloy into atubular shape, for example, and includes first to third housings 51 to53. Within the housing 24, first to eighth bearings 31 to 38 areaccommodated. The first to fifth bearings 31 to 35 and the seventh andeighth bearings 37 to 38 are each rolling bearings such as an angularcontact ball bearing, and the sixth bearing 36 is a rolling bearing suchas a needle rolling bearing.

The first housing 51 is formed in a tubular shape and configures adifferential mechanism housing for accommodating the transmission ratiovariable mechanism 5 as a differential mechanism, and configures a motorhousing for accommodating the transmission ratio variable mechanism-usemotor 23. One end of the first housing 51 is covered with an end wallmember 54. One end of the first housing 51 and the end wall member 54are fixed to each other by using a screwing member 55 such as a bolt. Aninner circumferential surface 56 at the other end of the first housing51 is fitted with an annular convex portion 57 at one end of the secondhousing 52. The first and second housings 51 and 52 are fixed to eachother by using a screwing member (not shown) such as a bolt.

The second housing 52 is formed in a tubular shape, and configures asensor housing for accommodating the torque sensor 44 and a resolverhousing for accommodating the motor resolver 43. Moreover, the secondhousing 52 accommodates therein a bus bar 99 (described later) of thetransmission ratio variable mechanism-use motor 23 and a lock mechanism58 for locking the rotor 231 of the transmission ratio variablemechanism-use motor 23. An outer circumferential surface 59 at the otherend of the second housing 52 is fitted with an inner circumferentialsurface 60 at one end of the third housing 53.

The third housing 53 is formed in a tubular shape, and configures areduction gear mechanism housing for accommodating the reduction gearmechanism 26. At the other end of the third housing 53, there isarranged an end wall section 61. The end wall section 61 is formed in anannular shape, and covers the other end of the third housing 53.

FIG. 3 is an enlarged view of the transmission ratio variable mechanism5 in FIG. 2 and a surrounding area thereof. With reference to FIG. 3,the input member 20, the output member 22, and the inner race 391 of thetransmission ratio variable mechanism 5 are each in an annular shape.

The input member 20 includes an input member main body 201 and a tubularmember 202 that is placed inward in a radial direction of the inputmember main body 201 and that is corotatably coupled to the input membermain body 201.

The first shaft 11, which is inserted through a through hole 202 a ofthe tubular member 202, is corotatably coupled to the tubular member202.

The second shaft 12, which is inserted through a through hole 22 a ofthe output member 22, is corotatably coupled to the output member 22.

Opposite end sections 11 a and 12 a of the both first shaft 11 and thesecond shaft 12 are supported coaxially and relatively rotatably by thesupport mechanism 133. The support mechanism 133 includes the tubularmember 202 and the eighth bearing 38. That is, the tubular member 202configures one portion of the input member 20 and configures one portionof the support mechanism 133.

The tubular member 202 surrounds the respective opposite end sections 11a and 12 a of the first and second shafts 11 and 12. One end of thetubular member 202 opposes the first bearing 31 in the radial direction.The other end of the tubular member 202 opposes the opposite end section12 a of the second shaft 12 in the radial direction.

The other end of the tubular member 202 is formed with a bearing holdinghole 109, and through the bearing holding hole 109, the opposite endsection 12 a of the second shaft 12 is inserted. Between the oppositeend section 12 a and the bearing holding hole 109 of the second shaft12, there is interposed the eighth bearing 38, which permits relativerotation between the tubular member 202 and the second shaft 12.

Moreover, the tubular member 202 may be corotatably coupled to theopposite end section 12 a of the second shaft 12, and also the eighthbearing 38 may be interposed between the tubular member 202 and theopposite end section 11 a of the first shaft 11.

The inner race 391 is placed outward in a radial direction of thetubular member 202. The outer race is held corotatably by an inclinedhole 63 formed in an inner circumferential section 233 of the rotor 231of the transmission ratio variable mechanism-use motor 23, and iscorotatable with the rotor 231 about the first axis A. The center lineof the inclined hole 63 is the second axis B.

Along with the rotation of the rotor 231 about the first axis A, thebearing ring unit 39 performs coriolis motion.

Moreover, the outer race of the bearing ring unit 39 may be coupleddifferentially rotatably to the input member 20 and the output member22, and also the inner race 391 may be coupled corotatably to the rotor231 of the transmission ratio variable mechanism-use motor 23. In thiscase, the bearing ring unit 39 makes an inner race support type.

FIG. 4 is a lateral side view of the transmission ratio variablemechanism 5 of which the one portion is expressed in cross section. Withreference to FIG. 3 and FIG. 4, when first concave-convex engagingsections 64 are arranged in the respective input member main body 201and inner race 391, the power can be transmitted between the inputmember main body 201 and the inner race 391. As second concave-convexengaging sections 67 are arranged in the respective inner race 391 andoutput member 22, the power can be transmitted between the inner race391 and the output member 22.

Each first concave-convex engaging section 64 includes a first convexportion 65 formed on a power transmission surface 70 as a one endsurface of the input member main body 201 and a first concave portion 66that is formed on a first end surface 71 as a one end surface of theinner race 391 and that is engaged with the first convex portion 65. Thepower transmission surface 70 and the first end surface 71 are opposedto each other in an axial direction S of the steering shaft 3. The firstconcave-convex engaging section 64 power-transmittably engages the powertransmission surface 70 and the first end surface 71. Moreover, thefirst concave portion 66 may be formed in an annular member formedseparately of the inner race main body, and the annular member may becorotatably held by the inner race main body. In this case, the innerrace main body and the annular member configure an inner race equivalentto the inner race 391. The placement of the first convex portion 65 maybe replaced by that of the first concave portion 66.

Each second concave-convex engaging section 67 includes a second convexportion 68 formed on a power transmission surface 72 as a one endsurface of the output member 22 and a second concave portion 69 that isformed on a second end surface 73 as the other end surface of the innerrace 391 and that is engaged with the second convex portion 68. Thepower transmission surface 72 and the second end surface 73 are opposedto each other in the axial direction S of the steering shaft 3. Thesecond concave-convex engaging section 67 power-transmittably engagesthe power transmission surface 72 and the second end surface 73.Moreover, the second concave portion 69 may be formed in an annularmember formed separately of the inner race main body, and the annularmember may be corotatably held by the inner race main body. In thiscase, the inner race main body and the annular member configure an innerrace equivalent to the inner race 391. The placement of the secondconvex portion 68 may be replaced by that of the second concave portion69.

FIG. 5 is a perspective view of the input member main body 201 and theinner race 391. With reference to FIG. 4 and FIG. 5, each first convexportion 65 is formed at regular intervals over the entire circumferenceof a circumferential direction C1 of the input member 20. Likewise, eachfirst concave portion 66 is formed at regular intervals over the entirecircumference of a circumferential direction C2 of the inner race 391.

For example, the number of first convex portions 65 to be formed is 38.The number of first concave portions 66 is different from that of thefirst convex portions 65. According to a difference between the numberof first convex portions 65 and that of first concave portions 66,differential rotation can be generated between the input member mainbody 201 and the inner race 391.

The second axis B of the inner race 391 is inclined by a predeterminedangle θ relative to the first axis A of the input member 20 and theoutput member 22. Thereby, some first convex portions 65 only out ofeach first convex portion 65 and some first concave portions 66 out ofeach first concave portion 66 only are meshed to each other.

FIG. 6 is a perspective view of the relevant parts of the input membermain body 201 and the inner race 391. With reference to FIG. 6, eachfirst convex portion 65 is formed integrally, by using a singlematerial, to the input member main body 201 of the input member 20,which is a corresponding member out of the input member 20, the innerrace 391, and the output member 22, that is, a member arranged with thefirst convex portion 65.

The first convex portion 65 and the input member main body 201 arecollectively molded. Examples of methods of molding the first convexportion 65 and the input member main body 201 include forging molding;casting molding; sinter molding: injection molding; metal injectionmolding; and cutting processing. In the metal injection molding, metalpowders are mixed with a binder so that injection molding can beperformed as in the case of plastic and after the injection molding, thebinder is removed by heating, and the resultant material is sintered toa metal single unit.

The first convex portion 65 entirely extends over the power transmissionsurface 70 with respect to a radial direction R1 of the input member 20,for example, and is formed in a semicircular shape in cross section. Thefirst convex portion 65 increases its cross sectional shape(semicircular shape) when seen from an inside of the radial direction R1toward an outside thereof. The first convex portion 65 is also in asemicircular shape about a center line E1 flush with the powertransmission surface 70 at any position in the radial direction R1. Withthe aforementioned configuration, the first convex portion 65progressively increases a width F1 with respect to the circumferentialdirection C1 of the input member 20 as a corresponding member when seenfrom the inside of the radial direction R1 toward the outside thereof,and has a progressively increasing protruding amount G1 from the powertransmission surface 70.

The base end section 74 of the first convex portion 65 is arranged withrelieving sections 75 for avoiding contact with the corresponding firstconcave portion 66. The relieving sections 75 are each formed at bothends of the first convex portion 65 with respect to the circumferentialdirection C1, and are configured by a trench allowing penetration of theinput member main body 201 in the radial direction R1. The arrangementof each relieving section 75 avoids contact between the first endsurface 71 of the first concave portion 66 of the inner race 391 and thefirst convex portion 65, undercut near the base end section 74 of thefirst convex portion 65 can be prevented from occurrence thereof.

Moreover, the arrangement of each relieving section 75 inhibits wearingof a metal molding part around each relieving section 75 when the inputmember main body 201 is molded by using the metal molding.

FIG. 7 is a cross-sectional view showing engagement between the firstconvex portion 65 and the first concave portion 66. With reference toFIG. 6 and FIG. 7, the first convex portion 65 is configured so thatcontact regions 76 of its external surface come in contact with acontact region 79 of the corresponding first concave portion 66. Eachcontact region 76 is arranged at a portion between the base end section74 and the leading end section 77 of the first convex portion 65.

The contact regions 76 are formed on both sides of the leading endsection 77. The position and the width of each contact region 76 aredetermined based on a contact angle α of the first convex portion 65.The contact angle α of the contact region 76 of the first convex portion65 is set within a range of between 15 and 75 degrees, for example.

The contact region 76 is formed by using a low friction material that isfor decreasing friction resistance. The low friction material contains amaterial having a friction coefficient lower than that of a material ofthe first convex portion 65. Examples of the low friction materialinclude diamond-like carbon (DLC), a nitride obtained by performing anitriding treatment on the first convex portion 65, a material obtainedby performing a curing coat treatment, and a low-μ coating material.

With reference to FIG. 6, a lubricant holding section 78 is formed at aportion near the contact region 76, out of the input member main body201. The lubricant holding section 78 is for holding lubricant such asgrease, and is formed on the power transmission surface 70 of the inputmember main body 201, for example.

The lubricant holding section 78 is formed by knurl, cross hatch,dimple, etc., for example, formed on the power transmission surface 70to have a roughened surface. The lubricant holding section 78 is formedby performing press molding, texturing, or shot peening processing onthe power transmission surface 70.

The lubricant holding section 78 is formed in at least one portion of aflat portion where the first convex portion 65 is not formed, out of thepower transmission surface 70. Moreover, the lubricant holding section78 may be formed in a portion where the contact region 76 is not formed,out of the first convex portion 65.

Each first concave portion 66 is formed integrally, by using a singlematerial, to the inner race 391 as a corresponding member out of theinput member 20, the inner race 391, and the output member 22, that is,a member arranged with the first concave portion 66.

The first concave portion 66 is molded in a manner similar to the waythat the above-described first convex portion 65 is molded.

The first concave portion 66 is formed in a shape approximately matchingthat of the first convex portion 65. Specifically, the first concaveportion 66 entirely extends over the first end surface 71 with respectto a radial direction R2 of the inner race 391, and is formed in asemicircular shape in cross section, for example. The first convexportion 66 increases its cross sectional shape (semicircular shape) whenseen from the inside of the radial direction R2 toward the outsidethereof. The first concave portion 66 is formed in a semicircular shapeabout a center line E2 flush with the first end surface 71 at anyposition in the radial direction R2. With the aforementionedconfiguration, the first concave portion 66 progressively increases awidth F2 with respect to the circumferential direction C2 of the innerrace 391 as a corresponding member from the inside of the radialdirection R2 toward the outside thereof, and has a progressivelyincreasing protruding amount G2 from the first end surface 71.

With reference to FIG. 6 and FIG. 7, the first concave portion 66 isconfigured so that the contact regions 79 on its surface come in contactwith the contact region 76 of the corresponding first convex portion 65.Each contact region 79 is arranged in a portion between an opening 80and a bottom 81 of the first concave portion 66. The contact regions 79are formed on both sides of the bottom 81. The position and the width ofeach contact region 79 are determined based on the preceding contactangle α.

The contact region 79 is formed by using a low friction material that isfor decreasing a friction resistance. Examples of the low frictionmaterial include a low friction material similar to that of the contactregion 76 of the first convex portion 65.

With reference to FIG. 6, a lubricant holding section 82 is formed at aportion near the contact region 79, out of the inner race 391. Thelubricant holding section 82 is for holding lubricant such as grease,and is formed on the first end surface 71 of the inner race 391, forexample.

The lubricant holding section 82 has a configuration similar to that ofthe lubricant holding section 78 of the power transmission surface 70 ofthe input member main body 201. The lubricant holding section 82 isformed in at least one portion of a flat portion where the first concaveportion 66 is not formed, out of the first end surface 71. Moreover, thelubricant holding section 82 may be formed in a portion where thecontact region 79 is not formed, out of the first concave portion 66.

Meanwhile, at least one of the lubricant holding section 78 near thefirst convex portion 65 and the lubricant holding section 82 near thefirst concave portion 66 may be abolished. Further, at least one of thecontact region 76 of the first convex portion 65 and the contact region79 of the first concave portion 66 may be formed without using the lowfriction material.

Further, as shown in FIG. 8, the first convex portion 65A may be formedso as to have the same cross sectional shape at any position in theradial direction R1 of the input member 20. Accordingly, the firstconcave portion 66A is formed so as to have the same cross sectionalshape at any position in the radial direction R2 of the inner race 391.

Also, as shown in FIG. 9, the cross section of the first concave portion66B may be formed in a gothic arch shape. In this case, the respectivecenter lines E3 and E4 of a first arcuate surface 83 and a secondarcuate surface 84 beside the bottom 81B of the first concave portion66B, are placed to be offset from each other. With the aforementionedconfiguration, the contact region 76 of the first convex portion 65 andthe contact region 79 of the first concave portion 66B can be made tomake more reliable contact.

With reference to FIG. 4, the power transmission surface 70 of the inputmember main body 201 and the first end surface 71 of the inner race 391may be respectively formed with bevel gears thereby to configure thefirst concave-convex engaging section. Also, the second end surface 73of the inner race 391 and the power transmission surface 72 of theoutput member 22 may be respectively formed with bevel gears thereby toconfigure a second concave-convex engaging section. In this case, thefirst convex portion and the second convex portion are configured byteeth of the bevel gears, respectively. The first concave portion andthe second concave portion are configured by grooves between the teethof the bevel gears, respectively.

With reference to FIG. 4 and FIG. 6, the second convex portion 68 of thesecond concave-convex engaging section 67 has a configuration similar tothat of the first convex portion 65 of the first concave-convex engagingsection 64. The second concave portion 69 has a configuration similar tothat of the first concave portion 66. More specifically, the powertransmission surface 72 of the output member 22 has a configurationsimilar to that of the power transmission surface 70 of the input membermain body 201. The second end surface 73 of the inner race 391 has aconfiguration similar to that of the first end surface 71 of the innerrace 391. Therefore, a detailed description of the second concave-convexengaging section 67 will be omitted.

With reference to FIG. 3 again, the rotor 231 of the transmission ratiovariable mechanism-use motor 23 includes a tubular shaped rotor core 85extending in the axial direction S and a permanent magnet 86 fixed onthe outer circumferential surface of the rotor core 85. Inward in theradial direction of the rotor core 85, the transmission ratio variablemechanism 5 and the torque sensor 44 are accommodated. By the rotor core85, both the first concave-convex engaging section 64 and the secondconcave-convex engaging section 67 of the transmission ratio variablemechanism 5 are surrounded over the entire circumference. The torquesensor 44 is also surrounded over the entire circumference. As thetransmission ratio variable mechanism 5 or the torque sensor 44 isaccommodated within the rotor core 85, the length of the housing 24 withrespect to the axial direction S can be shortened. As a result, animpact absorbing stroke for absorbing the impact by a secondary vehiclecollision can be secured long. Moreover, a placement space for a tilttelescopic mechanism (not shown) arranged adjacent to the housing 24 canalso be secured.

Examples of a material quality of the rotor core 85 include a steel, analuminum alloy, a clad material, and a resin material. When the cladmaterial which is a composite material formed by bonding together aplurality of types of metals is used, the oscillation can be inhibited.The use of the resin material in at least one portion of the rotor core85 results in light weight, which allows rotor inertia to decrease.

At one end of the rotor core 85, a held hole 87 is formed. Inward in theradial direction of the held hole 87, an annular bearing holding section88 is arranged. The bearing holding section 88 is placed in the annularconvex portion 89 formed on the inner circumferential side of one end ofthe first housing 51. The second bearing 32 is interposed between theheld hole 87 and the bearing holding section 88, thereby the one end ofthe rotor core 85 is rotatably supported by the first housing 51.

At an intermediate portion of the rotor core 85, a held hole 90 isformed. Inward in a radial direction of the held hole 90, an annularbearing holding section 91 is arranged. The bearing holding section 91is placed in an annular extending section 92 formed on the innercircumferential side of one end of the second housing 52. The annularextending section 92 is formed in a tubular shape extending from apartition wall 93 arranged at the other end of the second housing 52 toone S1 side of the axial direction S, and inserts through the rotor core85.

The fourth bearing 34 is interposed between the held hole 90 and thebearing holding section 91, thereby the intermediate portion of therotor core 85 is rotatably supported by the annular extending section 92of the second housing 52. By the second and fourth bearings 32 and 34 asa pair of bearings placed in a manner to sandwich the bearing ring unit39 in the axial direction of the rotor 231, the rotor core 85 isboth-end supported.

The permanent magnet 86 of the rotor 231 has polarities alternatelydifferent to each other in a circumferential direction C3 of thesteering shaft 3. N-poles and S-poles are alternately placed at regularintervals with respect to the circumferential direction C3. Thepermanent magnet 86 is fixed on the outer circumferential surface of theintermediate portion of the rotor core 85. The permanent magnet 86 andone portion of the transmission ratio variable mechanism 5 areoverlapped in position with each other with respect to the axialdirection S.

The stator 232 of the transmission ratio variable mechanism-use motor 23is accommodated within an annular first groove-shaped section 94 formedat the other end of the first housing 51. The first groove-shapedsection 94 is opened toward the other S2 side of the axial direction S.

The stator 232 includes a stator core 95 formed by stacking a pluralityof layers of electromagnetic steel plates and an electromagnetic coil96.

The stator core 232 includes a toroidal-shaped yoke 97 and a pluralityof teeth 98 that are placed at regular intervals in the circumferentialdirection of the yoke 97 and that are projecting inward in the radialdirection of the yoke 97. The outer circumferential surface of the yoke97 is fixed to the inner circumferential surface of the firstgroove-shaped section 94 of the second housing 52 by shrink fitting orany other similar technique. The electromagnetic coil 96 is wound aroundeach of the teeth 98.

On the other S2 side of the axial direction S relative to the stator232, the bus bar 99 is placed. The bus bar 99 is accommodated in thesecond housing 52 in a state of taking an entirely annular shape, and isconnected to each electromagnetic coil 96 of the transmission ratiovariable mechanism-use motor 23. The bus bar 99 supplies electric powerfrom the driving circuit to each electromagnetic coil 96. The bus bar 99and one portion of the third and fourth bearings 33 and 34 areoverlapped in position with respect to the axial direction S.

On the other S2 side of the axial direction S relative to the bus bar99, a lock mechanism 58 is placed. The lock mechanism 58 is forregulating the rotation of the rotor 231 of the transmission ratiovariable mechanism-use motor 23, and is accommodated at one end of thesecond housing 52.

The lock mechanism 58 includes a regulated section 100 corotatablycoupled to the rotor core 85, and a regulating section 101 forregulating the rotation of the regulated section 100 by being engagedwith the regulated section 100. The regulated section 100 is an annularmember. Concave portions 102 is formed on the outer circumferentialsurface of the regulated section 100. Each concave portion 102 is formedat one or a plurality of locations with respect to the circumferentialdirection of the regulated section 100. The concave portion 102 may bearranged in the rotor core 85. In this case, the rotor core 85configures the regulated section 100. One portion of the regulatedsection 100 is overlapped with one portion of the torque sensor 44 withrespect to a position in the axial direction S.

The regulating section 101 is placed opposite to each regulated section100 in the radial direction of the regulated section 100. The regulatingsection 101 is held by the second housing 52, and is movable to a sideof the regulated section 100. When the regulating section 101 moves tothe side of the regulated section 100 so as to be engaged with theconcave portion 102, the rotation of the rotor core 85 is regulated.

The motor resolver 43 is placed on the other S2 side of the axialdirection S relative to the lock mechanism 58. The motor resolver 43 isaccommodated in a second groove-shaped section 103 formed at one end ofthe second housing 52, and is positioned outward in the radial directionof the rotor core 85.

The second groove-shaped section 103 is an annular groove defined by anannular extending section 92 and an annular outer circumferentialsection 104 at one end of the second housing 52, and communicativelyconnects with the first groove-shaped section 94. An accommodating space139 for accommodating the transmission ratio variable mechanism-usemotor 23, the lock mechanism 58, and the motor resolver 43 is defined bythe first and second groove-shaped sections 94 and 103.

The motor resolver 43 and the torque sensor 44 are opposite to eachother in the radial direction R3 of the steering shaft 3. One portion ofthe motor resolver 43 and one portion of the torque sensor 44 areoverlapped in position with each other with respect to the axialdirection S. The motor resolver 43 includes a resolver rotor 105 and aresolver stator 106. The resolver rotor 105 is fixed corotatably on theouter circumferential surface 107 at the other end of the rotor core 85.The resolver stator 106 is fixed by a press fit on the innercircumferential surface 108 of the outer circumferential section 104 ofthe second housing 52.

The first bearing 31 rotatably supports the input member 20. The firstshaft 11 is rotatably supported by the first housing 51 via the tubularmember 202 and the first bearing 31 of the input member 20. The firstbearing 31 is surrounded by the second bearing 32, and the bothcomponents are overlapped in position with respect to the axialdirection S.

The third bearing 33 is interposed between a bearing holding hole 110formed in the inner circumferential section at the leading end of theextending section 92 of the second housing 52 and a bearing holdingsection 111 formed in the output member 22. The output member 22 isrotatably supported by the annular extending section 92 of the secondhousing 52 via the third bearing 33. The third bearing 33 is surroundedby the fourth bearing 34, and the both components are overlapped inposition with respect to the axial direction S.

A preload is respectively imparted to the first concave-convex engagingsection 64 and the second concave-convex engaging section 67. Thereby,smooth engagement between the first convex portion 65 and the firstconcave portion 66 and smooth engagement between the second convexportion 68 and the second concave portion 69 are respectively enabled.

A screw member 113 is placed in the inner circumferential section 112 atone end of the first housing 51. The screw member 113 configures abiasing member for biasing the input member main body 201 in a biasdirection H (the other S2 side of the axial direction S) in which theinput member main body 201 is brought close to the output member 22.Moreover, the screw member 113 configures a rigid member for rigidlysupporting the outer race 312 of the first bearing 31 with respect tothe axial direction S. The screw member 113 biases the input member mainbody 201 toward the output member 22, thereby to impart a preload to thefirst concave-convex engaging section 64 and the second concave-convexengaging section 67, respectively.

A male screw section 113 a formed on the outer circumferential surfaceof the screw member 113 is threaded onto a female screw section 134 a ofthe bearing holding hole 134 formed in the inner circumference of anannular convex portion 89 at one end of the first housing 51. Thereby,the screw member 113 biases (presses against) one end surface of theouter race 312 of the first bearing 31 held in the bearing holding hole134 of the first housing 51, in the bias direction H. The outer race 312of the first bearing 31 is rotatable to the bearing holding hole 134 andis relatively movable to the axial direction S. A lock nut 135 isarranged adjacent to the screw member 113. The lock nut 135 regulatesthe rotation of the screw member 113 in a state of being threaded ontothe female screw section 134 a.

The inner race 311 of the first bearing 31 is corotatably coupled to oneend of the tubular member 202 by being pressed fit thereinto or othersimilar techniques, and is corotatable to the input member main body 201and can be moved together therewith in the axial direction S via thetubular member 202. The inner race 311 comes into contact with one endsection of the input member main body 201 so as to press against theinput member main body 201 in the bias direction H.

Moreover, the first convex portion 65 of the first concave-convexengaging section 64 opposes the first concave portion 66 in the biasdirection H. Likewise, the second concave portion 69 of the secondconcave-convex engaging section 67 opposes the second convex portion 68in the bias direction H. The inner race 331 of the third bearing 33 isfixed to the output member 22 by a press fit. In the output member 22, astep section of its center portion contacts one end surface of the innerrace 331 so as to press against the inner race 331 in the bias directionH. The outer race 332 of the third bearing 33 is set at an annular stepsection 114 placed adjacent to the bearing holding hole 110 for movablyholding the outer race 332 into the bias direction H, whereby themovement in the bias direction H is regulated. The movement of theoutput member 22 in the bias direction H is regulated by the thirdbearing 33.

By the above-described configuration, the biasing force of the screwmember 113 is transmitted to the inner race 311 via the outer race 312and the rolling element of the first bearing 31, and further transmittedto the input member main body 201. The biasing force transmitted to theinput member main body 201 is transmitted to the first concave-convexengaging section 64 and the second concave-convex engaging section 67 inthis order, and further transmitted to the inner race 331, the rollingelement, and the outer race 332 of the third bearing 33. The biasingforce transmitted to the outer race 332 of the third bearing 33 isreceived by the annular step section 114.

Along with the movement of the inner race 391 of the bearing ring unit39 in the bias direction H by the biasing force of the of screw member113, the rolling element 393 of the bearing ring unit 39, the outerrace, and the rotor 231 of the transmission ratio variable mechanism-usemotor 23 are moved all together in the bias direction H.

Specifically, the outer race of the bearing ring unit 39 is fixed by apress fit to the inclined hole 63 of the rotor core 85. Thereby, therotor core 85 holds the outer race in a manner to rotate together aboutthe first axis A and to move together in the axial direction S.

Moreover, the respective outer races 322 and 342 of the second bearing32 and the fourth bearing 34 are loosely fitted to the correspondingannular held holes 87 and 90 of the rotor core 85, whereby the rotorcore 85 is supported relatively movably in the axial direction S. Theinner race 321 of the second bearing 32 is fixed by a press fit to thebearing holding section 88 of the annular convex portion 89. The innerrace 341 of the fourth bearing 34 is fixed by a press fit to the bearingholding section 91 of the annular extending section 92 of the secondhousing 52.

Moreover, by using the screw member 113, the output member 22 may bebiased in a bias direction (direction opposite to the bias direction H)in which the output member 22 is brought close to the input member mainbody 201. In this case, the screw member 113 is screwed into the bearingholding hole 110 for holding the third bearing 33. The biasing force ofthe screw member 113 is transmitted in the order of: the third bearing33, the output member 22, the second concave-convex engaging section 67,the first concave-convex engaging section 64, the input member main body201, the inner race 311 of the first bearing 31, the rolling element,and the outer race 312, and is received by the first housing 51.

The movement of the inner race 391 in the bias direction H will not beobstructed by the support mechanism 133. Specifically, the outer race382 of the eighth bearing 38 of the support mechanism 133 is looselyfitted to the bearing holding hole 109 of the tubular member 202, and isrelatively movable to the bearing holding hole 109 in the axialdirection S. The inner race 381 of the eighth bearing 38 is fixed by apress fit to the opposite end section 12 a of the second shaft 12.Moreover, the outer race 382 of the eighth bearing 38 may be fixed by apress fit to the bearing holding hole 109, loosely fitting the innerrace 381 to the opposite end section 12 a.

The torque sensor 44 is placed inward in the radial direction of therotor core 85 of the transmission ratio variable mechanism-use motor 23,and includes a multipole magnet 115 and magnetic yokes 116 and 117. Themultipole magnet 115 is fixed to the intermediate portion of the secondshaft. The magnetic yokes 116 and 117 are supported at one end of thethird shaft 13, as a pair of soft magnetic materials that form amagnetic circuit by being placed within a magnetic field generated bythe multipole magnet 115.

The multipole magnet 115 is a cylinder-shaped permanent magnet, and ismagnetized with a plurality of poles (equal in number between N-polesand S-poles) at regular intervals in the circumferential direction.

The magnetic yokes 116 and 117 are opposed to the multipole magnet 115with predetermined gaps in the radial direction of the multipole magnet115, and surround the multipole magnet 115. Each of the magnetic yokes116 and 117 is molded into a synthetic resin member 118. The syntheticresin member 118 is coupled corotatably to one end of the third shaft13.

The torque sensor 44 further includes a pair of magnetism collectingrings 119 and 120 for inducing a magnetic flux from the magnetic yokes116 and 117. The pair of magnetism collecting rings 119 and 120 are eachan annular member formed by using a soft magnetic material, and surroundthe magnetic yokes 116 and 117 so as to be magnetically linked to eachof the magnetic yokes 116 and 117.

The pair of magnetism collecting rings 119 and 120 are opposed to eachother to be spaced in the axial direction S. The magnetism collectingrings 119 and 120 are molded by the synthetic resin member 121. Thesynthetic resin member 121 is held by the annular extending section 92of the second housing 52.

The magnetic flux is generated in the magnetic yokes 116 and 117according to a relative rotation amount of the second and third shafts12 and 13. The magnetic flux is induced by the magnetism collectingrings 119 and 120, and is detected by a hole IC (not shown) buried inthe synthetic resin member 121. Thereby, it becomes possible to detect amagnetic flux density according to a torque applied to the second shaft12 (steering member).

With reference to FIG. 2, the fifth bearing 35 is placed on the other S2side of the axial direction S relative to the torque sensor 44. Thefifth bearing 35 is interposed between a bearing holding section 122formed in the outer circumference at one end of the third shaft 13 and abearing holding hole 123 formed on the partition wall 93 of the secondhousing 52. The bearing holding hole 123 rotatably supports one end ofthe third shaft 13 via the fifth bearing 35.

The third shaft 13 surrounds the second shaft 12 and the torsion bar 14.Specifically, the third shaft 13 has a through hole 124 opened to oneend of the third shaft 13. The other end of the second shaft 12 isinserted in the through hole 124. The second shaft 12 has a through hole125 extending in the axial direction S. The torsion bar 14 is insertedin the through hole 125.

One end of the torsion bar 14 is corotatably coupled to one end of thethrough hole 125 of the second shaft 12 by serration fitting or anyother similar technique. The other end of the torsion bar 14 iscorotatably coupled to the through hole 124 of the third shaft 13 byserration fitting or any other similar technique.

A space inward in the radial direction of the annular extending section92 of the second housing 52 is used as a torque sensor accommodatingchamber 126, and a structure for inhibiting intrusion of lubricant intothe torque sensor accommodating chamber 126 is further arranged.

One end of the torque sensor accommodating chamber 126 is closed by theseal-provided third bearing 33 placed at one end of the annularextending section 92 of the second housing 52, the output member 22placed inward in the radial direction of the third bearing 33, and thesecond shaft 12 placed inward in the radial direction of the outputmember 22. The other end of the torque sensor accommodating chamber 126is closed by the seal-provided fifth bearing 35, the third shaft 13placed inward in the radial direction of the fifth bearing 35, and thetorsion bar 14 for clogging the through hole 124 of the third shaft 13.

With the above-described configuration, it is possible to inhibit thelubricant filled in the respective first and second concave-convexengaging sections 64 and 67 from intruding into the torque sensoraccommodating chamber 126. Also, it is possible to inhibit the lubricantfilled in the engaging region of the worm shaft 27 and the worm wheel 28of the reduction gear mechanism 26 from intruding into the torque sensoraccommodating chamber 126.

The second shaft 12 and the third shaft 13 are supported relativelyrotatably to each other via the sixth bearing 36. The sixth bearing 36is surrounded by the worm wheel 28 of the reduction gear mechanism 26.The reduction gear mechanism 26 is accommodated in the accommodatingchamber 128 defined by the outer circumference section 127 and the endwall section 61 of the third housing 53, and the partition wall 93 ofthe second housing 52. One portion of the worm wheel 28 and the sixthbearing 36 are overlapped in position with respect to the axialdirection S.

The seventh bearing 37 is interposed between the intermediate portion ofthe third shaft 13 and the end wall section 61 of the third housing 53.The end wall section 61 rotatably supports the third shaft 13 via theseventh bearing 37.

The inner race 371 of the seventh bearing 37 is held by an annular stepsection 129 formed at the outer circumference section 127 of the thirdshaft 13 and a nut member 130 threaded onto the outer circumferencesection 127 of the third shaft 13. The outer race 372 of the seventhbearing 37 is held by an annular step section 131 formed in the thirdhousing 53 and a locating snap 132 held in the third housing 53.

Subsequently, one example of the operation of the motor vehicle steeringsystem 1 will be described. In the following description, three casesare described, that is, a case (i) that the rotation of the rotor 231 ofthe transmission ratio variable mechanism-use motor 23 is regulated; acase (ii) that the rotor 231 of the transmission ratio variablemechanism-use motor 23 is rotated and the input member 20 is notrotated; and a case (iii) that the rotor 231 of the transmission ratiovariable mechanism-use motor 23 is rotated and the input member 20 isrotated.

Any of the cases of (i), (ii), and (iii) is described as follows: thenumber of first convex portions 65 of the first concave-convex engagingsection 64 is 38 and the number of the first concave portions 66 thereofis 40, and the number of the second convex portions 68 of the secondconcave-convex engaging section 67 is 40 and the number of secondconcave portions 69 thereof is 40.

In the case of (i), that is, in a case that the rotation of the rotor231 of the transmission ratio variable mechanism-use motor 23 isregulated by the lock mechanism 58, the first convex portion 65 of theinput member main body 201 is rotated about the first axis A when thefirst shaft 11 is rotated by the operation of the steering member. Inthis case, the bearing ring unit 39 does not perform coriolis motion,that is, rotation about the first axis A, but the inner race 391 onlyrotates about the second axis B. This rotation rotates the inner race391 arranged with the first concave portion 66, and further rotates thesecond shaft 12.

As a result, when the input member 20 makes one rotation, the inner race391 makes 38/40 rotation, and the output member 22 makes 38/40 rotation.That is, the rotation of the input member 20 is decelerated to 19/20.

In the case of (ii), that is, in a case that the rotor 231 of thetransmission ratio variable mechanism-use motor 23 is rotated and theinput member 20 is not rotated due to a driver's holding the steeringmember, the rotor 231 is rotated about the first axis A, whereby thebearing ring unit 39 performs coriolis motion. Thereby, the inner race391 attempts to cause the input member 20 and the output member 22 toreversely rotate each other. However, because the rotation of the inputmember 20 is regulated, the output member 22 only is rotated.

In this case, as a result of the number of first concave portions 66being larger by two than the number of first convex portions 65, theinner race 391 is caused to advance its phase by an amount equivalent toa difference in the number of teeth (two) while the outer race of thebearing ring unit 39 makes one rotation. This results in the rotation ofthe inner race 391. As a result, when the outer race makes one rotation,the inner race 391 is rotated by an amount equivalent to the differencein the number of teeth and the output member 22 makes 2/40 rotations. Asdescribed above, the rotation of the rotor 231 of the transmission ratiovariable mechanism-use motor 23 is decelerated to 1/20, and theresultant rotations are output.

In the case of (iii), that is, in a case that the rotor 231 of thetransmission ratio variable mechanism-use motor 23 is rotated and theinput member 20 is rotated due to the driver steering the steeringmember, a rotation amount of the output member 22 makes a value obtainedby adding the rotation amount of the input member 20 (steering member)to the rotation amount of (ii).

Thereby, when the vehicle travels at a relatively low speed, thesteering angle θ1 may be amplified so as to exhibit a function ofassisting the steering of the driver.

Moreover, when the vehicle travels at a relatively high speed, thesteering angle θ1 and the vehicle yaw rate 7 may be compared, forexample, to determine a vehicle behavior. As a result, when the vehiclebehavior determined from the steering angle θ1 and the vehicle behaviordetermined from the detected yaw rate γ are not matched, the rotation ofthe rotor 231 of the transmission ratio variable mechanism-use motor 23may be increased or decreased in speed, whereby a vehicle stabilitycontrol (attitude stability control) is performed. Moreover, it may bealso possible to control driving of the rotor 231 of the transmissionratio variable mechanism-use motor 23 so that a counter steeringoperation is performed.

As described above, according to the embodiment, the first convexportion 65 of the first concave-convex engaging section 64 is integrallyformed in the input member main body 201, the first and second concaveportions 66 and 69 are integrally formed in the inner race 391, and thesecond convex portions 68 of the second concave-convex engaging section67 is integrally formed in the output member 22.

This reduces the number of components of the transmission ratio variablemechanism 5. Moreover, it is not necessary to separately prepare theholding members for respectively holding the first and second convexportions 65 and 68, and thus, the number of components of thetransmission ratio variable mechanism 5 can be further reduced. Further,as the number of components is small, the assembly of the transmissionratio variable mechanism 5 can be facilitated.

With the aforementioned configuration that the respective convexportions 65 and 68 and concave portions 66 and 69 are integrally formedin the corresponding members 201, 391, and 22, the accuracy forassembling the mutual components can be more easily enhanced as comparedto a case that the respective convex portions 65 and 68 and concaveportions 66 and 69 are formed separately of the corresponding members201, 391, and 22.

Further, because of the configuration that the respective convexportions 65 and 68 and concave portions 66 and 69 of the first andsecond concave-convex engaging sections 64 and 67, and the correspondingmembers 201, 391, and 22 are formed integrally by using a singlematerial, and thus, the respective convex portions 65 and 68 (respectiveconcave portions 66 and 69) and the corresponding members 201, 391, and22 can be collectively formed, the number of manufacturing process canbe reduced.

Moreover, the relieving section 75 is arranged at the base end section74 of the respective convex portions 65 and 68, and thus, when therespective convex portions 65 and 68 are engaged with the correspondingconcave portions 66 and 69, the respective first and second convexportions 65 and 68 are prevented from generation of undercut therein,whereby wearing of the respective convex portions 65 and 68 and concaveportions 66 and 69 can be decreased.

Further, out of the respective convex portions 65 and 68 and concaveportions 66 and 69, the more outward in the radial direction of thecorresponding members 201, 391, and 22, the wider the widths F1 and F2in the circumferential direction of the corresponding members 201, 391,and 22. As a result, the sliding of the both concave portions 66 and 69and corresponding convex portions 65 and 68 in mutual engagement can bereduced. Thereby, the durability of the respective convex portions 65and 68 and concave portions 66 and 69 can be made longer.

Moreover, corresponding lubricant holding sections 78 and 82 arearranged near the contact regions 76 and 79 of the respective convexportions 65 and 68 and concave portions 66 and 69. This enablessupplying of the lubricant to the contact regions 76 and 79 from nearthe respective contact regions 76 and 79, thereby making the engagementbetween the respective convex portions 65 and 68 and the correspondingconcave portions 66 and 69 more smooth.

Further, the contact regions 76 and 79 of the respective convex portions65 and 68 and concave portions 66 and 69 are formed by using a lowfriction material for decreasing a friction resistance. This furtherdecreases the friction resistance caused when the respective concaveportions 66 and 69 are engaged with the corresponding convex portions 65and 68.

The arrangement of the steering-assist-force imparting mechanism 19enables imparting of the steering assist force to the turning mechanism10, thereby reducing a force required by the driver for steering.

Among the inner race 391 and the outer race, the first and secondconcave-convex engaging sections 64 and 67 are arranged on the side ofthe inner race 391 that is relatively small in diameter. Thus, a supportspan in the radial direction can be shortened when the inner race 391 issupported from the both sides in the axial direction by the input member20 and the output member 22. This increases the supporting rigidity ofthe inner race 391.

Further, among the inner race 391 and the outer race, the concaveportions 66 and 69 of the first and second concave-convex engagingsections 64 and 67 are arranged on the side of the inner race 391 thatis relatively small in diameter. Thereby, the circumferential speed ofthe concave portions 66 and 69 arranged in the inner race 391 can bedecreased on driving. Thus, an engaging noise of the respective firstand second concave-convex engaging sections 64 and 67 can be decreased.

Moreover, the outer race of the bearing ring unit 39 is surrounded bythe rotor 231. Thus, it is possible to inhibit an engaging noise of therespective first and second concave-convex engaging sections 64 and 67from being transmitted to the outside of the rotor 231, thereby furtherdecreasing the noise.

The second axis B as a center line of the outer race can be inclined tothe first axis A by making the inclined hole 63 of the rotor core 85 ofthe rotor 23 hold the outer race.

Further, the rotor core 85 can be both-end supported by the second andfourth bearings 32 and 34. Thus, the supporting rigidity of the rotor231 can be increased. Also, the placement of the inner race 391 betweenthe second and fourth bearings 32 and 34 enables firmly supporting therotor core 85 for receiving the force from the inner race 391, therebythe rotor 231 is prevented from runout. As a result, it is possible tocontribute to a decrease in noise.

Further, by the eighth bearing 38, the mutual opposite end sections 11 aand 12 a of the first and second shafts 11 and 12 are mutuallysupported, and thus, the mutual coaxiality of the first and secondshafts 11 and 12 can be improved. As a result, the input member 20 andthe output member 22 are prevented from swinging of the shaft withrespect to others. A state of engagement between the convex portions 65and 68 and the corresponding concave portions 66 and 69 in therespective concave-convex engaging sections 64 and 67 is inhibited frombeing inadvertently changed, thereby contributing to decrease in anengaging noise.

The support mechanism 133 can be realized, moreover, by a simpleconfiguration using the tubular member 202 and the eighth bearing 38.Further, the arrangement of the eighth bearing 38 between the firstshaft 11 and the second shaft 12 enables a smooth relative rotation ofthe first and second shafts 11 and 12.

Further, the operation of the steering member 2 by a driver can becorrected by the transmission ratio variable mechanism 5. Thus, aso-called active steering in which a counter steering operation isautomatically performed by the transmission ratio variable mechanism 5is enabled, for example.

In each of the first concave-convex engaging section 64 arranged on theside of the first end surface 71 of the inner race 391 and the secondconcave-convex engaging section 67 arranged on the side of the secondend surface 73 of the inner race 391, preloads are imparted between therespective convex portions 65 and 68 and corresponding concave portions66 and 69. Thereby, in each of the first and second concave-convexengaging sections 64 and 67, the respective convex portions 65 and 68and corresponding concave portions 66 and 69 can be prevented fromgeneration of backlash between them, thereby decreasing the engagingnoise.

The inner race 391 is smaller in diameter than the outer race. Thus, thesupport span can be shortened in the radial direction where the innerrace 391 is supported from the both sides in the axial direction by theinput member 20 and the output member 22. Thereby a deformation of theinner race 391 can be decreased that results from the biasing force fromthe screw member 113. Thereby, a sufficient biasing force can be actedon the respective concave portions 66 and 69 formed in the inner race391. Thus, the respective first and second concave-convex engagingsections 64 and 67 can be reliably prevented from occurrence of backlashtherein.

Also, the screw member 113 biases the input member 20 toward the outputmember 22. Thereby, the biasing force of the screw member 113 can betransmitted in the order of: the input member 20; the firstconcave-convex engaging section 64 arranged on the side of the first endsurface 71 of the inner race 391; the second concave-convex engagingsection 67 arranged on the side of the second end surface 73 of theinner race 391; and the output member 22.

Further, the preload can be imparted by the screw member 113 to thefirst bearing 31. Thus, an abnormal noise resulting from the firstbearing 31 can be prevented from being generated.

The biasing force by the screw member 113 can be adjusted by adjustingthe screwing amount of the screw member 113 into the female screwsection 134 a.

Further, the biasing force of the screw member 113 can be transmitted tothe inner race 311 of the first bearing 31 via the outer race 312 of thefirst bearing 31. Thereby, the preload can be reliably imparted to thefirst bearing 31.

The force generated when the output member 22 unforcedly makes movementin the bias direction H can be received by the third bearing 33, andthus, the preload can be imparted to the third bearing 33.

The second and fourth bearings 32 and 34 support the rotor 231 movablyin the axial direction S. Thereby, along with the movement of the innerrace 391 by the biasing force of the screw member 113 in the axialdirection of the rotor 231, the outer race and the rotor 231 can bemoved together in the axial direction of the rotor 231. As a result, anunnecessary force can be prevented from being acted between the innerrace 391 and the outer race.

Further, the output of the transmission ratio variable mechanism 5 istransmitted via the steering-assist-force imparting mechanism 19 to theturning mechanism 10. In this configuration, when the output of thesteering-assist-force imparting mechanism 19 is transmitted to theturning mechanism 10, the output can be transmitted to the turningmechanism 10 without use of the transmission ratio variable mechanism 5.Thereby, the power input to the transmission ratio variable mechanism 5can be decreased, and thus, the transmission ratio variable mechanism 5can be made compact.

The input member 20, the inner race 391, and the output member 22 arealigned in a direction in which the first axis A extends (axialdirection S). Thereby, the transmission ratio variable mechanism 5 canbe made compact with respect to the radial direction of the input member20 and the output member 22 (radial direction R3). As a result, thetransmission ratio variable mechanism 5 can be made more compact.

Also, the rotor core 85 of the rotor 231 of the transmission ratiovariable mechanism-use motor 23 is formed in a tubular shape surroundingthe first and second concave-convex engaging sections 64 and 67.Thereby, the rotor 231 and the first and second concave-convex engagingsections 64 and 67 can be placed at a position overlapping with respectto the axial direction S. Thereby, further compactness of the motorvehicle steering system 1 can be achieved. The rotor 231 can be used asa soundproof wall. Thus, leaking of the engaging noise of the first andsecond concave-convex engaging sections 64 and 67 to the outside can beinhibited.

Further, as the torque sensor 44 is surrounded by the rotor core 85 ofthe rotor 231 of the transmission ratio variable mechanism-use motor 23,the rotor 231 and the torque sensor 44 can be placed at a positionoverlapping with respect to the axial direction S. As a result, furthercompactness of the motor vehicle steering system 1 can be achieved.

The transmission ratio variable mechanism 5 and thesteering-assist-force imparting mechanism 19 are arranged as steeringcolumns in the housing 24. As the housing 24 is assembled into thevehicle, the transmission ratio variable mechanism 5 and thesteering-assist-force imparting mechanism 19 can be collectivelyassembled into the vehicle. Moreover, the present invention offerssuperior noise reduction. Thus, even if the transmission ratio variablemechanism 5 and the steering-assist-force imparting mechanism 19 arearranged in the vehicle compartment where the housing 24 is placed,there is little influence from the driving noise.

The present invention is not limited to the contents of the embodimentdescribed above, and various modifications within a scope of the claimscan be made.

For example, the steering-assist-force imparting mechanism 19 in FIG. 1may be eliminated. In the following description, points different fromthose in the preceding embodiment are mainly described. Like referencenumerals are assigned in a similar configuration to omit description.

In this case, the driving circuit 41, the steering assisting motor 25,the reduction gear mechanism 26, the third shaft 13, the torsion bar 14,and the torque sensor 44 shown in FIG. 1 are eliminated. Further, theother end of the second shaft 12 is coupled to the universal joint 9.

In this case, as shown in FIG. 10, an end wall section 61C of a thirdhousing 53C is fixed to a second housing 52C in a state of being causedto run along the other end of the second housing 52C. In the thirdhousing 53C, no accommodating chamber for accommodating a reduction gearmechanism is arranged.

The second shaft 12C, which extends to the other end of the thirdhousing 53C and protrudes to the outside of the housing 24C, isconnected to a turning mechanism (not shown). An intermediate portion ofthe second shaft 12C is corotatably coupled with the inner race 371 ofthe seventh bearing 37.

As shown in FIG. 11, instead of the input member 20, it may be possibleto use an input member 20D formed so that an input member main body 201Dand a tubular member 202D are integrally formed by using a singlemember. The first convex portion 65 of the first concave-convex engagingsection 64 is integrally formed with the input member 20D as acorresponding member by using a single member.

A tubular member 202D and an output member 22D of the input member 20Dinclude opposite surfaces 136 and 137 that are opposed to each other.The opposite surfaces 136 and 137 are opposed to each other whilearranging a gap 138 in the axial direction S as a direction parallel tothe first axis A.

Thereby, when the input member 20D and the output member 22D come closeto each other by the biasing force of the screw member 113, the oppositesurfaces 136 and 137 can be prevented from contact with each other.

The input member 20D and the first convex portion 65 are formedintegrally by a single member. Thereby, the first convex portion 65 andthe input member 20D can be collectively formed. As a result, the numberof manufacturing process can be reduced.

Further, it may be possible to adopt a bearing ring unit 39 providedwith an outer race for differentially rotatably coupling the inputmember 20 and the output member 22 and an inner race for rotatablysupporting the outer race via a rolling element. Moreover, the presentinvention may be applicable to another general device other than themotor vehicle steering system.

1. A transmission ratio variable mechanism capable of changing atransmission ratio of a steered angle of steered wheels to a steeringangle of a steering member, comprising: an input member and an outputmember capable of rotation about a first axis; a first bearing ring,having first and second end surfaces, for differentially rotatablycoupling the input member and the output member to each other; a secondbearing ring for rotatably supporting the first bearing ring via arolling element; and an actuator capable of rotation-driving the secondbearing ring, wherein a second axis being a center line of the firstbearing ring and the second bearing ring is inclined to the first axis,wherein the input member and the output member respectively have powertransmission surfaces respectively opposite the first and the second endsurfaces of the first bearing ring, wherein a first concave-convexengaging section for power-transmittably engaging the first end surfaceof the first bearing ring and the power transmission surface of theinput member corresponding to the first end surface is arranged, whereinthe first concave-convex engaging section includes a first convexportion arranged on one of the first end surface and the powertransmission surface corresponding to the first end surface, and a firstconcave portion that is arranged on an alternate surface and that isengaged with the first convex portion, wherein a second concave-convexengaging section for power-transmittably engaging the second end surfaceof the first bearing ring and the power transmission surface of theoutput member corresponding to the second end surface is arranged, andwherein the second concave-convex engaging section includes a secondconvex portion arranged on one of the second end surface and the powertransmission surface corresponding to the second end surface, and asecond concave portion that is arranged on an alternate surface and thatis engaged with the second convex portion.
 2. The transmission ratiovariable mechanism according to claim 1, wherein the actuator comprisesan electric motor, and the electric motor includes a rotor forcorotatably holding the second bearing ring and capable of rotationabout the first axis.
 3. The transmission ratio variable mechanismaccording to claim 2, wherein the rotor is formed in a tubular shapesurrounding the first concave-convex engaging section and the secondconcave-convex engaging section.
 4. The transmission ratio variablemechanism according to claim 2, wherein the rotor is formed with aninclined hole, having a center line along the second axis, for holdingthe second bearing ring.
 5. The transmission ratio variable mechanismaccording to claim 2, wherein the rotor is both-end supported by asecond bearing and a fourth bearing held by a housing, and the firstbearing ring is placed between the second bearing and the fourth bearingwith respect to an axial direction of the rotor.
 6. The transmissionratio variable mechanism according to claim 5, wherein the secondbearing and the fourth bearing movably support the rotor with respect tothe axial direction of the rotor.
 7. The transmission ratio variablemechanism according to claim 1, further comprising: a first shaftinserted through a through hole formed in the input member andcorotatably connected to the input member; a second shaft insertedthrough a through hole formed in the output member and corotatablyconnected to the output member; and a support mechanism for coaxially,relatively rotatably supporting mutual opposite end sections of thefirst shaft and the second shaft.
 8. The transmission ratio variablemechanism according to claim 7, wherein the support mechanism includes:a tubular member that surrounds the mutual opposite end sections of thefirst shaft and the second shaft and that is corotatably coupled to oneof the first shaft and the second shaft; and a bearing, interposedbetween an alternate one of the first shaft and the second shaft and thetubular member, for permitting relative rotation of the both componentsthereof.
 9. The transmission ratio variable mechanism according to claim1, further comprising a biasing member for biasing in a bias directionin which one of the input member and the output member is brought closeto an alternate one of the input member and the output member, wherein apreload is imparted to the first concave-convex engaging section and thesecond concave-convex engaging section by the biasing member.
 10. Thetransmission ratio variable mechanism according to claim 9, wherein thebiasing member biases the input member toward the output member.
 11. Thetransmission ratio variable mechanism according to claim 9, furthercomprising a first bearing, held by a housing, for rotatably supportingthe input member, wherein the biasing member biases the input member viathe first bearing.
 12. The transmission ratio variable mechanismaccording to claim 11, wherein the first bearing is held by a bearingholding hole arranged in the housing, and the biasing member includes ascrew member engaged with a screw section formed in the bearing holdinghole.
 13. The transmission ratio variable mechanism according to claim12, wherein the first bearing includes an outer race held rotatably bythe bearing holding hole and movably in an axial direction along thefirst axis and an inner race that can be rotated and moved together inthe axial direction with the input member, and the screw member pressesagainst an end surface of the outer race.
 14. The transmission ratiovariable mechanism according to claim 11, further comprising a thirdbearing, held by the housing, for rotatably supporting the outputmember, wherein movement of the output member in a bias direction isregulated by the third bearing.
 15. The transmission ratio variablemechanism according to claim 1, wherein the convex portion and theconcave portion of each concave-convex engaging section are respectivelyformed integrally with a corresponding member, out of the input member,the first bearing ring, and the output member.
 16. The transmissionratio variable mechanism according to claim 15, wherein at least one ofa base end section of the first convex portion and a base end section ofthe second convex portion, a relieving section for avoiding contact witha corresponding concave portion is arranged.
 17. The transmission ratiovariable mechanism according to claim 1, wherein the input member, theoutput member, and the first bearing ring are respectively annularshaped, and the first convex portion, the second convex portion, thefirst concave portion, and the second concave portion respectivelyextend toward a radial direction and have a progressively increasingwidth with respect to a circumferential direction from an inside of theradial direction to an outside thereof.
 18. The transmission ratiovariable mechanism according to claim 1, wherein the first convexportion and the first concave portion include first contact regions thatcome into contact with each other, the second convex portion and thesecond concave portion include second contact regions that come intocontact with each other, and near the first contact regions and/or thesecond contact regions, lubricant holding sections are respectivelyarranged.
 19. A motor vehicle steering system, comprising: atransmission ratio variable mechanism according to claim 1; a steeringmember coupled to the input member; and a turning mechanism coupled tothe output member.
 20. The motor vehicle steering system according toclaim 19, further comprising a steering-assist-force imparting mechanismfor imparting a steering assist force.